1. Field of the Invention
The present invention relates to an image input apparatus, and relates more particularly to an image input apparatus arranged to read an image by performing scanning a plurality of times in the direction of sub-scanning, and also to a method for controlling the operation of the image input apparatus.
2. Description of Related Art
Image input apparatuses typically represented by image scanners are generally arranged to have a reading original (a sheet of paper, a book or the like) put on an original-placing board made of transparent glass, to cause an optical unit having a light source and an optical system and disposed in a space below the original-placing board to reciprocate in the direction of sub-scanning (in the direction of lines), and to lead light thus obtained from the original to a sensor which is composed of a CCD (charge-coupled device) or the like.
During recent years, the advancement of art of manufacturing semiconductors has come to permit a complex image processing operation to be easily carried out with an image input apparatus of the above-stated kind. For example, it is conceivable to read an original image by scanning the original image a plurality of times in the sub-scanning direction and to combine images thus obtained.
However, the conventional image input apparatus has presented the following problem. In the image input apparatus, a driving force of a motor is transmitted to a mechanism for moving the optical unit through a transmission means such as gears, which are in mesh with each other. These gears have a clearance or play between them. The clearance causes some backlash, which makes it difficult to cause an image input part to accurately reciprocate in the sub-scanning direction. Thus, the backlash tends to deteriorate precision in the sub-scanning direction to bring about an image discrepancy in the sub-scanning direction. Hence, resolution in the sub-scanning direction has sometimes decreased due to such backlash.